High speed materials sorting using x-ray fluorescence

ABSTRACT

A system and process for classifying a piece of material of unknown composition at high speeds, where the system connected to a power supply. The piece is irradiated with first x-rays from an x-ray source, causing the piece to fluoresce x-rays. The fluoresced x-rays are detected with an x-ray detector, and the piece of material is classified from the detected fluoresced x-rays. Detecting and classifying may be cumulatively performed in less than one second. An x-ray fluorescence spectrum of the piece of material may be determined from the detected fluoresced x-rays, and the detection of the fluoresced x-rays may be conditioned such that accurate determination of the x-ray fluorescence spectrum is not significantly compromised, slowed or complicated by extraneous x-rays. The piece of material may be classified by recognizing the spectral pattern of the determined x-ray fluorescence spectrum. The piece of material may be flattened prior to irradiation and detection. The x-ray source may irradiate the first x-rays at a high intensity, and the x-ray source may be an x-ray tube.

RELATED APPLICATION

[0001] This is a continuation application which claims priority under 35U.S.C. §120 to commonly-owned, co-pending U.S. patent application Ser.No. 09/400,491 entitled, “High Speed Materials Sorting Using X-RayFluorescence”, filed Sep. 21, 1999, which claims priority under 35U.S.C. §119(e) to U.S. provisional application serial No. 60/101,128entitled, “Electronics Sortation for Recyling of Post ConsumerNon-Ferrous Metals,” filed Sep. 21, 1998, where each application ishereby incorporated by reference in its entirety.

GOVERNMENT LICENSE RIGHTS

[0002] The U.S. Government has a paid-up license in this invention andthe right in limited circumstances to require the patent owner tolicense others on reasonable terms as provided for by the terms of GrantNo. DMI-9761412 awarded by the National Science Foundation.

[0003] This invention was made with Government support under Grant No.DMI-9761412 awarded by the National Science Foundation. The Governmenthas certain rights in this invention.

FIELD OF THE INVENTION

[0004] This invention relates to a system and process for sorting piecesof materials (by composition) in a stream of materials moving along aconveyor belt. Particularly; this invention relates to a system andprocess for classifying pieces of materials of unknown composition basedon the x-ray fluorescence spectrum of each respective piece so as topermit very high speed sorting of the unknown materials.

BACKGROUND OF THE INVENTION

[0005] Current worldwide environmental concerns have fueled an increasein efforts to recycle used equipment and articles containing materialsthat can be reused. Such efforts have produced new and improvedprocesses for sorting materials such as plastics, glass, metals, andmetal alloys.

[0006] As used herein, a “material” may be a chemical element, acompound or mixture of chemical elements, or a compound or mixture of acompound or mixture of chemical elements, wherein the complexity of acompound or mixture may range from being simple to complex. Materialsmay include metals (ferrous and non-ferrous), metal alloys, plastics,rubber, glass, ceramics, etc. As used herein, element means a chemicalelement of the periodic table of elements, including elements that maybe discovered after the filing date of this application.

[0007] Generally, methods for sorting pieces of materials involvedetermining a physical property or properties of each piece, andgrouping together pieces sharing a common property or properties. Suchproperties may include color, hue, texture, weight, density,transmissivity to light, sound, or other signals, and reaction tostimuli such as various fields. Methods to determine these propertiesinclude visual identification of a material by a person, identificationby the amount and/or wavelength of the light waves emitted ortransmitted, eddy-current separation, heavy-media plant separation, andx-ray fluorescence detection.

[0008] With respect to metals and metal alloys, today it is neithertechnically nor commercially feasible to separate and recover many ofthe non-ferrous metals that are manufactured into products and discardedat the end of their useful life. In residential waste, only aluminumcans are recycled to any significant degree. Virtually none of the othernon-ferrous materials in our residential waste are recovered. Instead,they are disposed in landfills. Further, small non-ferrous materialsbelow ⅝ inches in size are landfilled from nearly 200 automobileshredders.

[0009] Smaller-sized pieces of non-ferrous metals from automobileshredders are not separated because their recovery is notcost-effective. They can only be consolidated and shipped to largerfacilities for further processing. Mixed non-ferrous metals fromindustrial processes are often disposed or junked because hand-sortingand small-particle recovery technologies either do not work well or arenot cost-effective. Nearly 2 billion pounds of valuable non-ferrousmetals are discarded in landfills every year in the U.S. alone.Worldwide, the amount of metal wasted is far greater. If this metalcould be economically recycled at high volumes, the potential valuegenerated is estimated to be in excess of 1 billion dollars (U.S.) peryear. Further, there are approximately 200 waste-to-energy facilities,200 automobile shredders, and thousands of metal scrap yards in the U.S.alone that could benefit financially (and otherwise) from an improvedsorting system.

[0010] X-ray fluorescence spectroscopy has long been a useful analyticaltool in the laboratory for classifying materials by identifying elementswithin the material, both in academic environments and in industry. Theuse of characteristic x-rays such as, for example, K-shell or L-shellx-rays, emitted under excitation provides a method for positiveidentification of elements and their relative amounts present indifferent materials, such as metals and metal alloys. For example,radiation striking matter causes the emission of characteristic K-shellx-rays when a K-shell electron is knocked out of the K-shell by incomingradiation and is then replaced by an outer shell electron. The outerelectron, in dropping to the K-shell energy state, emits x-ray radiationcharacteristics of the atom.

[0011] The energy of emitted x-rays depends on the atomic number of thefluorescing elements. Energy-resolving detectors can detect thedifferent energy levels at which x-rays are fluoresced, and generate anx-ray signal from the detected x-rays. This x-ray signal may then beused to build an energy spectrum of the detected x-rays, and from theinformation, the element or elements which produced the x-rays may beidentified. Fluorescent x-rays are emitted isotopically from anirradiated element and the detected radiation depends on the solid anglesubtended by the detector and any absorption of this radiation prior tothe radiation reaching the detector. The lower the energy of an x-ray,the shorter the distance it will travel before being absorbed by air.Thus, when detecting x-rays, the amount of x-rays detected is a functionof the quantity of x-rays emitted, the energy level of the emittedx-rays, the emitted x-rays absorbed in the transmission medium, theangles between the detected x-rays and the detector, and the distancebetween the detector and the irradiated material.

[0012] Although x-ray spectroscopy is a useful analytical tool forclassifying materials, with current technology, the cost is high peranalysis, and the time required is typically minutes or hours. Scrapyard identification of metals and alloys is primarily accomplished todayby trained sorters who visually examine each metal object one at a time.Contamination is removed by shearing. A trained sorter observes subtlecharacteristics of color, hue, texture, and density to qualitativelyassess the composition of the metal. Sometimes, spark testing orchemical “litmus” testing aids in identification. The process is slowand inaccurate, but is the most common method in existence today forsorting scrap metal to upgrade its value.

[0013] There have been disclosed a variety of systems and techniques forclassifying materials based on the x-ray fluorescence of the material.Some of these systems involve hand-held or bench-top x-ray fluorescencedetectors. Some of these systems include serially conveying pieces ofmaterial along a conveyor belt and irradiating each piece, in turn, withx-rays. These x-rays cause each piece of material to fluoresce x-rays atvarious energy levels, depending on the elements contained in the piece.The fluoresced x-rays are detected, and the piece of material is thenclassified based on the fluoresced x-rays and sorted in accordance withthis classification.

[0014] Such disclosed systems, however, have not been widely acceptedcommercially because they require about one second or more to detect thex-rays and accurately classify the piece of material accordingly, andthey are expensive relative to the number of objects identified per unittime.

SUMMARY OF THE INVENTION

[0015] In response to the need for faster classification, disclosedherein is a system and process for classifying a piece of material basedon the x-ray fluorescence of its constituents, wherein x-rays aredetected from the piece and the piece is accurately classified,cumulatively, in substantially less than a second—indeed, typically inabout 100 milliseconds (ms) or less.

[0016] To achieve these speeds, a high intensity x-ray source, such asan x-ray tube, is used to irradiate the piece. The previously mentionedsystems, by contrast, employ a comparatively low-power narrow-spectrumx-ray source such as, for example, Cadmium isotope Cd¹²⁹, Americiumisotope Am²⁴¹, Cobalt isotope Co⁵⁷, and Iron isotope Fe⁵⁵. Although useof an x-ray tube has been mentioned as a possible alternative x-raysource for a material sorting system, a high intensity x-ray source hasnot been implemented by others in such systems, and there are majorproblems in doing so that have not previously been resolved.Consequently, there previously has not been shown a system that enablesuse of a high intensity x-ray source in such a system.

[0017] Another problem with many known material sorting systems thatclassify pieces of material based on the x-ray fluorescence of thematerial is that such systems are limited to analyzing only thefluorescence of specific, predetermined elements of interest in thepiece of material. Analyzing only select fluorescence limits theaccuracy of the identification and the range of materials that can beidentified.

[0018] In response to this problem, there is also disclosed herein asystem and process for classifying a piece of material based on thex-ray fluorescence of the piece by recognizing a broad spectral patternof the x-ray fluorescence.

[0019] According to the invention, a high speed process for classifyinga piece of material of unknown composition is provided. The piece isirradiated with x-rays from an x-ray source, causing the piece tofluoresce x-rays. The fluoresced x-rays are detected with an x-raydetector and the piece is classified from the detected fluorescedx-rays.

[0020] In optional illustrative embodiments, detecting and classifyingare cumulatively performed in less than one second, less than 500 ms,less than 100 ms, less than 50 ms, and preferably even less than 15 ms.

[0021] Preferably, but optionally, an x-ray fluorescence spectrum of thepiece of material from the detected fluoresced x-rays is determined, andat least one of the steps of the irradiating and detecting includesconditioning the irradiating x-rays or the fluoresced x-rays,respectively, such that speed and accuracy of determining the x-rayfluorescence spectrum is not significantly compromised or complicated bygeneration or detection of extraneous x-rays.

[0022] In yet another optional aspect, the irradiating x-rays arefiltered to reduce a number of irradiating x-rays having an energy leveltoo low to cause the piece to fluoresce x-rays having an energy levelwithin a predefined range of the x-ray fluorescence spectrum.

[0023] In still another optional aspect, the irradiating x-rays areaimed at the piece of material to reduce an amount of x-rays detected bythe x-ray detector that were not fluoresced by the piece itself.

[0024] In still another optional aspect of the illustrated embodiments,the x-ray fluorescence spectrum is determined for a predefined range ofenergy levels, and the irradiating x-rays are aimed by collimating thex-ray source with a collimator whose aperture components are madesubstantially of one or more materials that fluoresce at energy levelsnot within the predefined range.

[0025] For example, the operative parts of the collimator may be formedessentially of polyvinyl chloride.

[0026] In another optional aspect, the x-ray source is aimed at thepiece of material with a small aperture to substantially confine thex-rays detected by the x-ray detector to those fluoresced by the pieceand limit detection of other x-rays.

[0027] In another optional aspect, the x-ray detection is aimed bycollimating the x-ray detector with a collimator consisting essentiallyof one or more materials that fluoresce at energy levels not within thepredefined range. For example, the collimator may be formed essentiallyof polyvinyl chloride.

[0028] In yet another optional aspect, the piece of material is conveyedon a conveyor through a detection area where the irradiating x-raysirradiate the piece and the fluoresced x-rays are detected from thepiece. The conveyor may be formed essentially of one or more materialsthat fluoresce at energy levels not within the predefined energy range,so that the conveyor does not fluoresce x-rays that significantlyinterfere with determination of the x-ray fluorescence spectrum of thepiece.

[0029] In another optional aspect, the spectral pattern of thedetermined x-ray fluorescence spectrum is recognized.

[0030] In still another optional aspect, a plurality of x-rayfluorescence spectra are stored as reference spectra on acomputer-readable medium, each reference spectrum having a spectralpattern and corresponding to a different material classification.Recognizing the detected spectral pattern includes comparing thedetermined x-ray fluorescence spectrum to each of the reference spectrato determine which reference spectrum has a spectral pattern mostsimilar to the spectral pattern of the determined x-ray fluorescencespectrum. The piece of material is classified as the materialclassification corresponding to the reference spectrum determined tohave the most similar spectral pattern.

[0031] In a further optional aspect, the piece of material is conveyedon a conveyor and through a detection area where the irradiating x-raysirradiate the piece and the fluoresced x-rays are detected from thepiece, and an ejector corresponding to the classification of the pieceis actuated such that the piece is ejected from the conveyor at a pointdownstream from the detection area and associated with saidclassification.

[0032] In another optional aspect, the piece of material is flattenedprior to irradiation and detection.

[0033] In still another optional aspect, the step of irradiatingincludes irradiating the x-rays at a high intensity.

[0034] Optionally, but preferably, the x-ray source is an x-ray tube.

[0035] It will be appreciated that both large and small pieces may beprocessed, including pieces having a largest dimension less than ⅝ inch;indeed, even less than approximately ¼ inch.

[0036] In another illustrative embodiment, a system for classifying apiece of material of unknown composition is provided, where the systemis connected to a power supply. An x-ray source powered by the powersupply generates x-rays that irradiate the piece of material, causingthe piece to fluoresce x-rays. An x-ray detector detects the fluorescedx-rays and produces as an output a signal, called an x-ray signal,representing the detected x-rays. An x-ray fluorescence processingmodule is connected to the x-ray detector. The processing modulereceives as an input the x-ray signal and generates as an output aclassification signal that identifies the classification of the piece ofmaterial.

[0037] In optional aspects, the x-ray detector and x-ray fluorescenceprocessing module are operative to detect the fluoresced x-rays andclassify the piece, respectively, in a combined time less than onesecond, less than 500 ms, less than 100 ms, less than 50 ms, andpreferably even less than 15 ms.

[0038] In yet another optional aspect, the x-ray fluorescence processingmodule includes a spectrum acquisition module connected to the x-raydetector, the spectrum acquisition module receives as an input the x-raysignal and generates as an output an x-ray fluorescence spectrum, and aclassification module receives as an input the x-ray fluorescencespectrum and generates as an output a classification signal indicating aclassification of the piece of material. The system is conditioned suchthat accurate determination of the x-ray fluorescence spectrum is notsignificantly compromised or complicated by generation or detection ofextraneous x-rays.

[0039] In another optional aspect of this embodiment, the x-rayfluorescence spectrum is determined for a predefined range of energylevels, and an x-ray filter filters the irradiating x-rays to reduce anumber of irradiating x-rays having an energy level too low to cause thepiece to fluoresce x-rays having an energy level within the predefinedrange of the x-ray fluorescence spectrum.

[0040] In another optional aspect the output of the x-ray source isconditioned by a collimator, the collimator having an aperture to aimthe irradiating x-rays at the piece such that production of x-rays fromobjects other than the piece is reduced.

[0041] In an optional feature of this aspect, the x-ray fluorescencespectrum is determined for a predefined range of energy levels, aperturecomponents of the collimator being made substantially of one or morematerials that fluoresce at energy levels not within the predefinedrange.

[0042] For example, the collimator may be formed essentially ofpolyvinyl chloride.

[0043] In another optional aspect, the x-rays detected by the x-raydetector are conditioned by a collimator, the collimator having anaperture to aim the detection of the fluoresced x-rays at the pieceduring the detection such that detection of incident radiation fromobjects other than the piece is minimized.

[0044] For example, the collimator may be formed essentially ofpolyvinyl chloride.

[0045] In still another optional aspect, the x-ray fluorescence spectrumis determined for a predefined range of energy levels, and a conveyorconveys the piece of material through a detection area where theirradiating x-rays irradiate the piece and the fluoresced x-rays aredetected from the piece, and the conveyor consists essentially of one ormore materials that fluoresce at energy levels not within the predefinedrange.

[0046] For example, the conveyor belt may be formed essentially ofpolyvinyl chloride.

[0047] In another optional aspect, the x-ray fluorescence processingmodule includes a spectrum acquisition module connected to the x-raydetector, the spectrum acquisition module to receive as an input thex-ray signal and to generate as an output an x-ray fluorescencespectrum, and a classification module to receive as an input the x-rayfluorescence spectrum and to generate as an output a classificationsignal that indicates the classification of the piece, wherein theclassification module is operative to classify the piece by recognizinga spectral pattern of the x-ray fluorescence spectrum.

[0048] In yet another optional aspect, a computer-readable storagemedium stores a plurality of x-ray fluorescence spectra as referencespectra, each reference spectrum having a spectral pattern andcorresponding to a different material classification, and theclassification module further includes means for comparing thedetermined x-ray fluorescence spectrum to each of the reference spectrato determine which reference spectrum has a spectral pattern mostsimilar to the spectral pattern of the determined x-ray fluorescencespectrum. The classification of the piece corresponds to the referencespectrum determined to have the most similar spectral pattern.

[0049] In a further optional aspect, a conveyor conveys the piece ofmaterial through a detection area where the irradiating x-rays irradiatethe piece and the fluoresced x-rays are detected from the piece, and anejector corresponding to the classification of the piece having an inputreceives an ejection signal, and the ejector ejects the piece from theconveyor in accordance with the ejection signal at a point downstreamfrom the detection area and associated with said classification.

[0050] In another optional aspect, the piece of material is flattenedprior to irradiation and detection.

[0051] In still another optional aspect, the x-ray source is operativeto generate the irradiating x-rays at a high intensity.

[0052] Optionally, but preferably, the x-ray source is an x-ray tube.

[0053] In another illustrative embodiment, a system for classifying apiece of material of unknown composition at high speeds is provided. Thesystem includes means for irradiating the piece with x-rays from anx-ray source, causing the piece to fluoresce x-rays, means for detectingthe fluoresced x-rays with an x-ray detector, and means for classifyingthe piece of material from the detected fluoresced x-rays.

[0054] In optional illustrative embodiments, the means for detecting andmeans for classifying are operative to detect the fluoresced x-rays andclassify the piece, respectively, in a combined time of less than onesecond, less than 500 ms, less than 100 ms, less than 50 ms, andpreferably even less than 15 ms.

[0055] Preferably, but optionally, the system includes means fordetermining an x-ray fluorescence spectrum of the piece of material fromthe detected fluoresced x-rays, and means for conditioning at least oneof the irradiating x-rays and the fluoresced x-rays, respectively, suchthat speed and accuracy of determining the x-ray fluorescence spectrumis not significantly compromised or complicated by generation anddetection of extraneous x-rays.

[0056] In yet another optional aspect, the means for conditioningincludes means for filtering the irradiating x-rays to reduce a numberof irradiating x-rays having an energy level too low to cause the pieceto fluoresce x-rays having an energy level within a predefined range ofthe x-ray fluorescence spectrum.

[0057] In another optional aspect of the illustrated embodiments, themeans for conditioning includes means for aiming the irradiating x-raysat the piece of material to reduce an amount of x-rays detected by thex-ray detector that were not fluoresced by the piece itself.

[0058] Preferably, but optionally, the means for aiming includes acollimator whose aperture components are made substantially of one ormore materials that fluoresce at energy levels not within the predefinedrange.

[0059] For example, operative parts of the collimator may be formedessentially of polyvinyl chloride.

[0060] In another optional aspect, the means for conditioning includesmeans for aiming the x-ray detector at the piece of material tosubstantially confine the x-rays detected by the x-ray detector to thosefluoresced by the piece and limit detection of other x-rays.

[0061] In another optional aspect, the x-ray fluorescence spectrum isdetermined for a predefined range of energy levels, and the means foraiming the x-ray detector includes a collimator whose aperturecomponents are made of one or more materials that fluoresce at energylevels not within the predefined range.

[0062] For example, operative parts of the collimator may be formedessentially of polyvinyl chloride.

[0063] In yet another optional aspect, the system further includes meansfor conveying the piece of material through a detection area where theirradiating x-rays irradiate the piece and the fluoresced x-rays aredetected from the piece, and the means for conveying includes a conveyorthat may be formed essentially of one or more materials that fluoresceat energy levels not within the predefined energy range of thedetermined x-ray fluorescence spectrum so that the conveyor does notfluoresce x-rays that significantly interfere with determination of thex-ray fluorescence spectrum of the piece.

[0064] In an optional aspect, the conveyor is made essentially ofpolyvinyl chloride.

[0065] In still another optional aspect, the system further includesmeans for recognizing the spectral pattern of the determined x-rayfluorescence spectrum, and the means for classifying the piece base theclassification on the recognition of the spectral pattern.

[0066] In another optional aspect, the means for detecting, means fordetermining, means for recognizing, and means for classifying areoperative to detect the fluoresced x-rays, determine the x-rayfluorescence spectrum, recognize the spectral pattern of the x-rayfluorescence spectrum, and classify the piece, respectively, in acombined time of less than one second.

[0067] In a further optional aspect, the system further includes meansfor storing a plurality of x-ray fluorescence spectra as referencespectra on a computer-readable medium, each reference spectrum having aspectral pattern and corresponding to a different materialclassification, and the means for recognizing the detected spectralpattern includes means for comparing the determined x-ray fluorescencespectrum to each of the reference spectra to determine which referencespectrum has a spectral pattern most similar to the spectral pattern ofthe determined x-ray fluorescence spectrum, and the piece of material isclassified as the material classification corresponding to the referencespectrum determined to have the most similar spectral pattern.

[0068] In yet another optional aspect, the system further includes meansfor flattening the piece of material prior to irradiation and detection.

[0069] In still another optional aspect, the system further includesmeans for irradiating the x-rays at a high intensity.

[0070] Optionally, but preferably, the x-ray source is an x-ray tube.

[0071] In another optional aspect, the system further includes means forconveying the piece of material through a detection area where theirradiating x-rays irradiate the piece and the fluoresced x-rays aredetected from the piece, and means for actuating an ejectorcorresponding to the classification of the piece such that the piece isejected from the conveying means at a point downstream from thedetection area and associated with said clarification.

[0072] These and other features and advantages of the invention will bemore readily understood and appreciated from the detailed descriptionbelow, which should be read together with the accompanying drawingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] In the drawings:

[0074]FIG. 1 is a diagram showing an illustrative embodiment of a highspeed material sorting system;

[0075]FIGS. 2A and 2B are a flow chart showing an illustrativeembodiment of a process of sorting pieces of material at high speed;

[0076]FIG. 3 is a diagram showing an illustrative embodiment of an x-raydetection chamber of a high speed material sorting system;

[0077]FIG. 4 is a block diagram showing an illustrative embodiment of anx-ray fluorescence processing module;

[0078]FIG. 5 is a data flow diagram showing an illustrative embodimentof the function of a spectrum acquisition module;

[0079]FIG. 6 is a flow chart showing an illustrative embodiment of aprocess for classifying a piece of material based on the x-rayfluorescence spectrum of the piece;

[0080]FIG. 7A is a diagram showing an illustrative embodiment of usingan energy histogram to represent an x-ray fluorescence spectrum;

[0081]FIG. 7B is a diagram showing an illustrative embodiment of usingan energy histogram to represent an x-ray fluorescence spectrum;

[0082]FIG. 8 is a screen capture of an illustrative embodiment of a userinterface for analyzing detected x-ray fluorescence spectra; and

[0083]FIG. 9 is a block diagram showing an illustrative embodiment of aprocess of binary sorting materials.

DETAILED DESCRIPTION

[0084] The combination of the high speed x-ray irradiation and detectiontechniques and the execution of a complex sorting algorithm describedherein permit highly accurate classification and sorting of materials atvery fast rates, at least one to two orders of magnitude faster thancurrently used techniques.

[0085]FIG. 1 depicts an illustrative embodiment of a high speed materialsorting system. A materials singulator and feeder 3 feeds a singulatedstream of pieces of material 11 onto a conveyor belt 5. The conveyorbelt 5 receives the pieces of material 11 and conveys the pieces ofmaterial through an x-ray detection chamber 7 downstream to be sortedinto sorting bins 18-23. Although a conveyor belt is used in theillustrative embodiment of FIG. 1, any suitable conveying means may beused.

[0086] An x-ray detection chamber 7 receives each piece of material,irradiates the material with x-rays, and detects the x-ray fluorescence(xrf) from the materials as a result of the irradiation. The detectionchamber 7 is also connected to an xrf processing module 9 through asignal carrier 8 such as, for example, a data bus. The xrf processingmodule 9 receives a signal representing the xrf detected from a piece ofmaterial along the signal carrier 8. The xrf processing module 9 thenclassifies the piece of material based on the xrf signature of thematerial, and activates a sorting device such as an air jet—for example,one of the air jets 13-17—that is mapped or assigned to theclassification. When one of the air jets 13-17 receives a signal fromthe xrf processing module 9, that air jet emits a stream of air thatcauses a piece of material to be ejected from the conveyor belt 5 into asorting bin corresponding to that air jet such as, for example, one ofthe sorting bins 18-22. High speed air valves from Mac Industries may beused, for example, to supply the jets with air pressure at, for example,60-90 psi, with operating/closing times of 15 ms.

[0087] Although air jets are used to eject materials in the illustrativeembodiment of FIG. 1, other methods may be used to eject the pieces ofmaterial, such as robotically removing the piece of material from belt5, pushing the piece of material from belt 5, or causing an opening inthe belt from which a piece of material may drop.

[0088] In addition to sorting bins 18-22, into which pieces of materialare forced, the system 1 may also include a sorting bin 23 that receivespieces of material not forced from the belt 5. A piece of material maynot be ejected from the belt 5 when the classification of the piece isnot determined. Thus, sorting bin 23 may serve as a default bin intowhich unclassified pieces of materials are dumped. Alternatively,sorting bin 23 may be used to receive one or more classifications ofpieces of material by deliberately not assigning any of the sorting bins18-22 to the one or more classifications. This technique of defaultsorting can be particularly useful in sorting materials which fluoresceat low energy levels difficult to detect because of absorption by airsuch as, for example, aluminum.

[0089] Depending upon the classifications of materials desired, multipleclassifications may be mapped to a single air jet and sorting bin. Inother words, there need not be a one-to-one correlation betweenclassifications and sorting bins. For example, it may be commerciallybeneficial to sort copper and brass into the same sorting bin. Toaccomplish this sort, when a piece of material is classified as eithercopper or brass, the same air jet may be activated to sort both copperand brass into the same sorting bin. The contents of this sorting binmay, for example, then be used to create a copper/brass alloy. Suchcombination sorting may be applied to produce any desired combination ofmaterial pieces and element distribution. The mapping of classificationsmay be programmed in the sorting application 35 of FIG. 4 to producesuch desired combinations.

[0090] The classifications of pieces are user-definable and not limitedto any known classification of materials. The classifications may bedefined by using appropriate reference spectra, and programming thethreshold values for these spectra, as is described in more detail belowin connection with FIGS. 4 and 6. For example, the classification may bebetween: plastics, ceramics, glass, and, metals, such classificationhaving a relatively broad scope; different metals and metal alloys suchas, for example, zinc, copper, brass, chromeplate, and aluminum, suchclassification having a narrower scope; or between specific grades ofsteel, such classification having a relatively narrow scope. Thus, theclassifications may be programmed to distinguish between materials ofsignificantly different compositions such as, for example, plastics andmetal alloys, or to distinguish between materials of almost identicalcomposition such as, for example, different grades of steel.

[0091] Although FIG. 1 shows an illustrative embodiment of a high speedmaterial sorting system in which the pieces of materials 1 are conveyedalong a straight and level path, the system described herein is notlimited to such an embodiment. In an alternative embodiment, theconveyor belt 5 may be divided into multiple belts in series such as,for example, two belts, where a first belt conveys the materials intothe detection chamber 7, and a second belt conveys the pieces ofmaterial from the detection chamber 7. For example, the second belt maybe at a lower height than the first belt, such that pieces of material11 fall from the first belt onto the second belt through the detectionchamber.

[0092] In an illustrative embodiment, an x-ray detector and x-ray sourcemay be arranged such that the irradiation of x-rays onto or detectedfrom the belt(s) is kept to a minimum (i.e., an acceptably low level),thus reducing detection of extraneous x-rays from the belt(s). (Thisboth improves the speed and accuracy of classification as well as avoids“flooding” the detection needlessly.) In yet another embodiment, duringconveyance through the detection area each piece of material may be slidacross a window of material or air gap that allows x-rays to passthrough, with the x-ray source situated to irradiate x-rays through thewindow.

[0093] In another illustrative embodiment, the part of the conveyer beltdownstream from the detection chamber may be replaced by a circularconveyor, and the air jets 13-17, or other suitable removal means,arranged along the exterior or interior of the circular conveyor. In anoptional aspect of this illustrative embodiment, the entire conveyorbelt 5 is a circular conveyor, where the pieces of materials are fedonto the conveyer, and a detection chamber is located at a point alongthe conveyor.

[0094] In another illustrative embodiment of the high speed materialsorting system, gravity may be used to accelerate the speed of thepieces of materials. For example, the conveying belt may convey piecesof material onto a surface that slopes downward leading toward thedetection chamber 7. Further, at some point along the path ofconveyance, the pieces of materials may be dropped into free fall, andbe irradiated during free fall from an x-ray source or sources locatedalong the sides. The fluoresced x-rays could also be detected duringfree fall from an x-ray detector or detectors located along the path oftrajectory. Although such an arrangement reduces background radiation,the detection process becomes more complex. The location and speed ofeach falling piece must be detected to properly time the sorting process(constant speed cannot be assumed as in the previously discussedembodiments). Further, the inherent unstable nature of pieces rollingdown a slope or in free fall introduces a variable element into thesorting process.

[0095] The system and process for classifying described herein may beapplied to a handheld system for classifying pieces of material one at atime. In such a system, adjustments would have to be made forportability, but the general methods described herein for irradiatingwith x-rays, detecting fluoresced x-rays, building an xrf spectrum, andrecognizing a spectral pattern of the xrf spectrum may be used.

[0096]FIGS. 2A and 2B is a flow chart depicting an exemplaryillustrative embodiment of a process of sorting materials at highspeeds. First, in step 51, materials are fed in a singulated stream ontoa conveyor belt. In an optional aspect of this illustrative embodiment,the materials are flattened with a flattening apparatus before being fedonto the conveyor belt 5. For example, a rolls crusher may be used forthis purpose.

[0097] By flattening the piece of material, any other materials adheredto the piece of material may be removed. Further, flattening a piece ofmaterial before feeding the piece onto the conveyor belt improvessorting and classification of the materials. First, flattened pieces ofmaterial remain stationary on the conveyor belt, and do not roll. Thus,in the illustrative embodiment of FIG. 1, when a piece of material isclassified, and an appropriate air jet 13-17 is actuated, the piece isin a position anticipated by the xrf processing module 9, and the pieceis ejected from the conveyor belt into the appropriate sorting bin18-22. Second, flattening the pieces of material provides a largersurface area to irradiate and from which to detect x-rays. Consequently,the piece of material is bombarded with and fluoresces more x-rays,resulting in a more complete xrf spectrum being determined for the pieceof material. Third, the composition of the piece of material is lessinfluenced by surface contaminants. Because during flattening, freshmaterial surfaces are exposed, a cleaner xrf spectrum is produced.Consequently, the spectra detected are more representative of the pieceof material and not other materials that may be adhering to the surfaceof the piece of material.

[0098] In an illustrative embodiment, the conveyor belt 5 is depressedor troughed in the center such that pieces of materials gravitate to thecenter of the conveyor belt 5, where they remain more stationary and maybe aligned directly beneath a detector.

[0099] Next, in step 53, the materials are conveyed along the conveyorbelt and into an x-ray detection chamber. In an illustrative embodiment,each piece is flattened while being conveyed along the belt, asdiscussed above in connection with step 51.

[0100] In an illustrative embodiment, the belt is comprised at leastmostly of a material such as, for example, polyvinyl chloride (PVC),that when irradiated, fluoresce x-rays only at low energy levels, aswill be disclosed in more detail with connection to FIG. 4. The speed atwhich the belt is operated is programmed in accordance with the spacingbetween the pieces of material and the cumulative time which it takesto: acquire or detect the x-rays from a piece of material; determine anxrf spectrum; and classify the piece. Such speeds may exceed 100 inchesper second.

[0101] In step 55, when a piece of material has entered the x-raydetection chamber, the piece is irradiated with x-rays, as will bediscussed below in more detail in connection to FIG. 4. The exposure tox-rays causes each material to fluoresce x-rays at various energylevels, producing an xrf spectrum. In step 57, this xrf spectrum isdetected by an x-ray detector.

[0102] Next, in step 59, for each piece of material, the material isclassified based on the xrf that was detected, as discussed in moredetail below in connection to FIG. 3.

[0103] Next, in step 61 of FIG. 2B, an air jet corresponding to theclassification of the piece is activated. Between the time at which thepiece of material was irradiated and the time at which the air jet isactivated, the piece of material has moved from the detection chamber toa point downstream from the detection chamber, at the rate of conveyingof the belt. In an embodiment, the activation of the air jet is timedsuch that as the piece passes the air jet mapped to the classificationof the piece, the air jet is activated and the piece of material isejected from the conveyor belt.

[0104] In an alternative embodiment, the activation of air jet is timedby a respective position detector that detects when a piece of materialis passing before the air jet and sends a signal to enable theactivation of the jet. In step 63, the sorting bin corresponding to theair jet that was activated receives the ejected piece of material.

[0105]FIG. 3 is a diagram illustrating an illustrative embodiment of thex-ray detection chamber 7. A power supply 45 supplies power to an x-raysource 47. For example, the power supply may be a Spellman RMP 300 powersupply, and the x-ray source 47 is an x-ray tube such as, for example, awater-cooled Varian OEG-50 x-ray tube. Such an x-ray tube and powersupply combination is capable of operating at up to 300 watts at 30 kv.In an illustrative embodiment, the x-ray tube is operated at 13-17 kv atlevels in the range of 1-10 watts.

[0106] The intensity of x-rays is proportional to the rate at whichx-rays are transmitted. Although commercially available x-ray sourcesusing radioactive isotopes, for example Cd¹²⁹, Am⁴¹, and Co⁵⁷, and Fe⁵⁵may be used as the x-ray source 47, as is common in material sortingsystems that detect xrf, such isotope-based sources do not producex-rays at the intensity that can be produced by an x-ray tube. Thenumber of x-rays fluoresced 26 from a piece of material 25 irradiatedwith x-rays 24 is a function of the intensity and energy levels of theirradiating x-rays 24. Thus, when an x-ray source 47 is used thatproduces less intense x-rays 24, less x-rays 26 are fluoresced from thepiece of material 25. Consequently, fluoresced x-rays 26 must bedetected from the piece of material 25 for a longer period of time sothat an xrf spectrum with a strong enough image, i.e. a recognizablespectral pattern, may be determined.

[0107] Therefore, to increase the speed of detection and classification,an x-ray tube may be used as the x-ray source 47. An x-ray tube iscapable of producing x-rays several orders of magnitude more intensethan any commercially available isotope-based x-ray sources. Thisintensity is particularly important when the piece of material 25 isrelatively small, when the x-ray source 47 is a relatively long distanceaway from the piece of material 25, or when the piece of material 25 isa relatively long distance away from the detector 27, the reasons forwhich are discussed in more detail below. Further, an x-ray tube has theadded advantage of being capable of being turned off when not in use, incontrast to a radioactive isotope. As used herein, the term “highintensity” when used to describe x-rays means x-rays of an intensity atleast an order of magnitude more intense than the x-rays produced from atypical, commercially-available isotope-based x-ray source.

[0108] Using an x-ray tube, or another comparable high intensityradiation source, as the x-ray source 47, however, causes massiveamounts of x-rays to be present in the x-ray chamber 7, orders ofmagnitude more than would be present if an isotope-based source wereused. The presence of this amount of x-rays causes problems with thedetection of x-rays by the x-ray detector 27 and the determination of anaccurate xrf spectrum. Therefore, the irradiation and detection of thex-rays must be conditioned as described in more detail below.

[0109] In an illustrative embodiment, the x-ray source 47 is collimatedby a collimator 49, having an aperture which is aimed at a detectionarea where a particular piece of material 25 is to be irradiated. In anillustrative embodiment, the detection area is approximately a circlewith a diameter of about 2.5″. As used herein, a “collimator” is adevice having an aperture which limits the transmission of x-rays of anx-ray stream such that the x-rays move in the same, or nearly the same,direction.

[0110] An x-ray detector 27 detects the x-rays fluoresced from the pieceof material 25, and sends a signal representing the detected x-raysalong the signal carrier 8 to the xrf processing module 9. In anillustrative embodiment, the x-ray detector 27 is collimated by acollimator 29. An aperture of collimator 29 aims x-ray detector 27 atthe piece of material 25 during detection such that detector 27 directlyreceives fluoresced x-rays 26 from piece of material 25 while extraneousx-rays including x-rays 24 irradiated from x-ray source 47 andincidental x-rays from other objects within the detection chamber 7 areinhibited by collimator 29 from reaching detector 27, thereby reducingdetection of these extraneous x-rays by detector 27. These direct andincidental x-rays are referred to herein as background noise. Backgroundnoise includes x-rays fluoresced or reflected from objects in thechamber 7 other than the piece of material 25, including: the interiorsurfaces of the chamber 7 itself; items used to fasten together sectionsof the chamber 7 itself; the conveyor belt 5; or any other objectspresent in the chamber. Such background noise may be caused by theirradiating x-rays 24 and fluoresced x-rays 26 impacting other objectsin the chamber 27 and causing secondary fluorescence.

[0111] In an illustrative embodiment in which a high intensity x-raysource 47 is used, the high intensity x-rays 24 bombarding the piece ofmaterial 25 cause the piece of material 25 to fluoresce x-rays 26 ofhigh intensity. Because of these high intensity x-rays, it is necessaryto use an x-ray detector 27 capable of handling the high intensity xrfwithout flooding. An example of an x-ray detector capable of handlingthe high intensity fluorescence x-rays is the Amptek XR-100T with Si-PINdiode detector and beryllium window to admit low energy x-rays. Theenergy resolution of the Amptek detector is 250 ev or 0.25 Kev. However,improved x-ray detectors are currently being developed which are capableof even smaller (more precise) energy resolution. Thus, the choice ofresolution of an xrf spectrum is a function of the resolution desiredand the resolution capability of the x-ray detector 27.

[0112] In an illustrative embodiment, the x-ray detector 27 is highlysensitive, and when too many x-rays impact the x-ray detector 27, it maybecome flooded with fluoresced x-rays. Such flooding may cause the x-raydetector 27 to malfunction or reduce the accuracy of the determined xrfspectrum. When too many x-rays impact the x-ray detector 27, theaccuracy of the spectrum determination may be reduced because not all ofthe fluoresced x-rays 26 will be detected. Thus, in an illustrativeembodiment, accurate classification is best achieved by generatingx-rays 24 at an intensity that will not cause the x-ray detector 27 tobe flooded by irradiation. Thus, the x-ray 47 source may be operated atpower levels to produce relatively low intensity radiation such as, forexample, at 13.5 V and 0.03 mA, giving an x-ray power output of only 0.4watts.

[0113] The x-rays 24 emitted by the x-ray source 47 may be filtered byan x-ray filter. Such filtering is beneficial when an x-ray source 47that has a broadband energy output (emits x-rays of a wide range ofenergy levels) for example, an x-ray tube, is used. Such broadbandenergy includes unneeded x-rays that produce increased background noisein the x-ray detection chamber 7. Unneeded irradiated x-rays areirradiated x-rays of an energy level insufficient to cause the piece ofmaterial 25 to fluoresce x-rays within an energy range of the determinedxrf spectrum. For example, if the determined x-ray spectrum isprogrammed to have an energy range between 5 kev and 30 kev, then onlyfluoresced x-rays 26 within this range are relevant for classificationof the piece 25. Generally, to cause the fluorescence of an x-ray at agiven energy level, an impacting irradiated x-ray must have an energylevel equal to or greater than the given energy level. Thus, to causethe fluorescence of an x-ray of between 5 kev and 30 kev, an impactingirradiated x-ray must have an energy level of at least 5 kev. Thus, anyx-rays irradiated 24 from the x-ray source 47 that are less thanapproximately 5 kev are unneeded. The term extraneous x-rays, as usedherein, includes both background noise and unneeded irradiated x-rays.The unneeded x-rays may cause additional background noise, and theunneeded x-rays alone or in combination with the background noise mayflood the x-ray detector 27. Thus, an x-ray filter may be used to reducethe number of unneeded x-rays impacting the piece of material 25 orimpacting the x-ray detector 27.

[0114] As discussed above, in an illustrative embodiment using a highenergy x-ray source, such as an x-ray tube, a high amount of backgroundnoise is generated. Although typically a conveyor belt made of some sortof rubber material is used in sorting systems, the intensity of thex-rays 24 generated from the x-ray source 47 cause even elements presentin a rubber belt to emit x-rays. Therefore, in an illustrativeembodiment, the belt preferably is made of a material that will notfluoresce x-rays at energy levels that fall within the range of theenergy spectrum being detected, thereby interfering with the energyspectrum. The energy level of the fluoresced x-rays depends on theenergy levels at which the elements present in the piece of material 25fluoresce. The energy level at which an element fluoresces isproportional to its atomic number. For example, elements of low atomicnumbers fluoresce x-rays at lower energy levels. Thus, the material forthe conveyor belt may be chosen such that the belt comprises elements ofcertain atomic numbers that do not fluoresce x-rays within a certainenergy range. For example, PVC contains chloride which fluoresces at alow energy level, and therefore, when an xrf spectrum with a relativelyhigh energy range is being determined, PVC may be a good choice as amaterial for the conveyor belt.

[0115] For the same reasons as discussed above with respect to theconveyor belt 5, the x-ray detection chamber 7, or at least the interiorsurface of the x-ray detection chamber 7, may be made or lined with amaterial that fluoresces at particular energy levels such as, forexample, PVC. Further, the collimator 49 for the x-ray source 47 may bemade of a material that fluoresces at particular energy levels such as,for example, PVC.

[0116] X-ray chambers, such as x-ray chamber 7, are typically shieldedwith a layer of lead along the interior surface to absorb the x-rays andthus protect persons in the vicinity of the x-ray chamber. In a highspeed material sorter, however, when a high intensity x-ray source suchas an x-ray tube is used, if the intensity is high enough, the leaditself begins to fluoresce x-rays at a level that may interfere with thedetector. If there are enough x-rays fluoresced from the lead, the x-raydetector may be flooded, and the accuracy of the determined xrf spectrummay be reduced. To reduce the probability of flooding the x-ray detector27, the x-ray chamber 7 may be lined with a material, for example, PVC,that fluoresces x-rays at lower energy levels at which the x-rays have ahigher probability of being absorbed by air.

[0117] Besides reducing the accuracy of the xrf spectrum by flooding,the xrf spectrum may be further compromised by incorrectly indicatingthat the piece of material 25 contains lead, or a different amount oflead than is correct, which may lead to incorrect classification. Such asituation would arise if lead fluoresced within the energy spectrumbeing determined. In such a situation, to avoid loss of x-rayfluorescence spectrum accuracy, lead should not be used to line theinterior surface of the x-ray chamber.

[0118] In an illustrative embodiment, the xrf detected by the x-raydetector 27 is collimated by a collimator 29. The collimator 29 limitsthe effects of extraneous x-rays being received by the x-ray detector27, by aiming the detector 27 at the detection area where the x-rays 26are fluoresced by the piece of material 25. In an illustrativeembodiment, this collimator 29 is made of a material or materials thatfluoresces at particular energy levels such as, for example, PVC, forthe same reasons discussed above with respect to collimator 49, x-raychamber 7, and conveyor belt 5.

[0119] Thus, when using an x-ray source 27 of high intensity, such as anx-ray tube, the irradiation and detection of the x-rays may beconditioned in order to accurately detect the xrf of a piece of materialand accurately classify the piece. Conditioning the irradiated x-raysmay include collimating the x-ray source 49 and filtering the x-rays 24produced by the x-ray source 47. Conditioning the detection of x-raysmay include collimating the x-ray detector 27, and using materials thatfluoresce at low energy levels for many of the components proximate todetection area such as, for example, the conveyor belt 5 and the x-raychamber 7.

[0120] For high speed sorting of materials using an x-ray source thatproduces x-rays of high intensity, collection intervals for collectingx-ray spectra may range lower than 10 ms (ms). Longer intervals such as,for example, 5 seconds, may be used to collect reference spectra thatare stored for comparison against detected spectra. Generally, thelong-time spectra are less noisy than the shorter duration samples sincerandom variations of the fluorescing and detection of x-rays thus of theoutput of the detector 27, tend to cancel over time.

[0121] In the illustrative embodiment of FIG. 3, the x-ray source 47 islocated above the detection area. In alternative illustrativeembodiments, the x-ray source may be located to the side of detectionarea, or beneath the belt. Locating the x-ray source beneath thedetection area, however, requires maintaining a surface, perhaps aportion of the belt, through which the x-rays must penetrate toirradiate the piece of material 25. In such an illustrative embodiment,the belt may have a mesh configuration, or may have apertures throughwhich x-rays may pass through the belt impeded mainly by the x-rayabsorption of air. Further, the composition of the belt may be such thatthe belt is largely transparent to the transmission of x-rays. Althoughlocating the x-ray source beneath the detection area requiresmaintaining a surface, such an arrangement does place the x-ray detectorcloser to materials, regardless of the size of the materials. Thisarrangement therefore may increase the number of irradiating x-rays thatimpact the piece of materials, resulting in an increased number ofx-rays fluoresced and an increased number of detected x-rays.

[0122]FIG. 4 is a diagram illustrating an illustrative embodiment of thexrf processing module 9. The x-ray detector 27 sends a signal thatcarries the xrf detected from the piece of material 25 along a signalcarrier 8. The xrf signal is amplified by amplifier 31 to produce anamplified xrf signal transmitted on signal carrier 10 which is receivedby a spectrum acquisition module 33. In an illustrative embodiment, theamplifier 31 is an A250 preamplifier that conditions the signal toproduce the amplified xrf signal on signal carrier 10.

[0123]FIG. 5 is a data flow diagram illustrating an illustrativeembodiment of the function of the spectrum acquisition module 33. Thespectrum acquisition module 33 receives the amplified xrf signal andconverts the amplified xrf signal into a discrete energy histogramspectrum 34. In an illustrative embodiment, the spectrum acquisitionmodule comprises an Amptech MCA 5000 acquisition card and softwareprogrammed to operate the card at a real-time rate. The Amptech MCA cardhas 2048 channels for dispersing x-rays into a discrete energy spectrumwith 2048 energy levels. In this illustrative embodiment, for eachcollection interval, the energy count for each energy level may bestored in a separate collection register. A processor of the xrfprocessing module 9 may then read each collection register to determinethe number of counts for each energy level during the collectioninterval, and build the energy histogram. The processor interfaces tothe Amptech card by executing I/O reads and writes across a bus such as,for example, an ISA bus. In this illustrative embodiment, the generalprocedure for obtaining a spectrum is: load timer registers, issue startcollection command, wait for done status, and copy the collectionregisters to a computer-readable memory.

[0124] The sorting application 35, also referred to herein as theclassification module, executes a sorting algorithm that classifies thepiece of material 25 by recognizing the spectral pattern of the xrfspectrum of the piece. FIG. 6 is a flow chart showing an illustrativeembodiment of step 59 of FIG. 2A for classifying the piece based on thexrf spectrum of the material. In step 59, each energy count of the xrfspectrum is normalized such that each energy count may be considered adimensional component of an xrf unit vector. Accordingly, each energycount is reduced by an amount equal to:$\frac{1}{\sqrt{( {a^{2} + b^{2} + {c^{2}\ldots \quad n^{2}}} )}}$

[0125] where a, b, c and n are energy counts at various energy levels.

[0126] The energy range of the xrf spectrum determined by the spectrumacquisition module 33, the number of energy levels of the determined xrfspectrum, and the resolution of the determined xrf spectrum are allprogrammable. These parameters may be chosen depending on the sort to beperformed. If a large range of materials are being sorted, the energyrange may be large and the number of energy levels high. If pieces ofmaterials are to be sorted have relatively similar compositions, thenthe resolution may be fine, so as to distinguish between the spectralpatterns. For example, when pieces of metal are to be sorted intoaluminum, brass, chrome plated zinc, copper, stainless steel, and zinc,the spectrum acquisition module 33 may be programmed to detect and countx-rays at 256 energy levels ranging from 0 kev to 25.6 kev with 0.1 kevresolution.

[0127] Next, in step 63, the vector dot products are computed betweenthe normalized detected xrf spectrum and the normalized xrf spectra ofany stored reference materials. Prior to starting the sorting process, aset of reference samples is collected and the xrf spectra of thesesamples determined and stored, for example, in a non-volatile storagemedium 41. In an illustrative embodiment, for reference spectra, thex-ray spectrum of each reference material is collected over an intervalof 5 seconds.

[0128] To compute the dot product, if the detected normalized referencespectra has normalized energy counts of a₁, a₂, . . . a₂₅₆, and thenormalized xrf spectrum of a reference material has normalized energycounts of b₁, b₂, . . . b₂₅₆, then the vector dot product between thesetwo spectra would be a₁×b₁+a₂×b₂+ . . . a₂₅₆×b₂₅₆. Because all thespectra have been normalized to a unit vector, the dot products betweentwo identical spectra would produce the value 1, where the results ofall dot products should be between the 1 and 0. A dot product of 0results if for every energy level of the detected spectrum for which atleast a single count is detected, the reference spectrum does not have asingle energy count, or vice versa.

[0129] A user interface 37 provides functions to sample, view, andcompare individual spectrums to prepare the reference material set andto designate which references will be “active” and read into fastervolatile memory for use during execution of the sorting algorithm. Thus,the xrf processing module computes a vector dot product between thenormalized xrf of the detected material and the normalized xrf spectrumof each of the active reference materials.

[0130] Next, in step 65, it is determined whether any of the computedvector dot products reach a minimum threshold value. In an illustrativeembodiment, there is a single minimum threshold value that must beachieved for any of the reference spectra. In an alternativeillustrative embodiment, each reference spectrum has an individualminimum threshold value that the dot product calculated for thereference spectrum must equal or exceed. Having an individual thresholdvalue for each reference spectrum adds additional flexibility indistinguishing between similar spectral patterns, as is discussed inmore detail below.

[0131] The threshold values for reference spectra are programmable by asystem user. The closer the spectral patterns of two reference spectra,the higher the threshold value for these reference spectra should beprogrammed in order to positively distinguish the two spectra. Forexample, if a user is only interested in distinguishing between a firstspectral pattern that has several peaks at certain energy levels, and asecond spectral pattern that has energy peaks at certain other energylevels, then the user may program the threshold value for these tworeference spectra to be relatively low to distinguish between the twospectral patterns (although the threshold value should be high enough todistinguish the two reference spectra from other reference spectra).Conversely, if two spectral patterns have energy peaks that share commonenergy levels and where, for these energy levels, the normalized countvalue for each spectra is close to the other, then the threshold valueshould be set relatively high. The value of the threshold must be sethigh enough so that the spectral pattern of a detected piece of materialmust be very close to matching one of the two reference spectra for aclassification to be made. This high threshold ensures correctrecognition of a spectral pattern.

[0132] If it is determined in step 65 that at least one vector dotproduct reaches a minimum threshold value, then at step 67 it isdetermined which computer dot product value has the highest value. Thedot product of the highest value indicates the reference spectra closestto the detected spectra. In an alternative illustrative embodiment,where each spectrum has an individual threshold value, it is determinedfor which of the reference spectra the highest dot product wascalculated for which the minimum threshold for the reference materialwas reached.

[0133] Consequently, in step 69, the classification corresponding to thestored spectrum that produced the highest dot product and equals orexceeds a minimum threshold is determined. Such a classification may beencoded on a classification signal. In an alternative illustrativeembodiment of step 69, the classification corresponding to the storedspectrum whose dot product exceeds the spectrum's threshold value by thegreatest percentage is selected. For example, assume spectra A has athreshold of 0.4 and spectra B has a threshold of 0.6. In addition,assume a dot product of 0.7 is calculated for spectra A and a dotproduct of 0.8 is calculated for spectra B. The classificationcorresponding to Spectra A would be selected even though Spectra B's dotproduct is higher because Spectra A's dot product is 75% over itsthreshold, while Spectra B's dot product is only 33% over its threshold.

[0134] Classifying a piece of material by comparing the spectral shapeor spectral pattern of the xrf of a spectrum contrasts to known methodsof analyzing only energy counts of select peak energy levels. Such knownmethods merely determine whether the number of counts for select energylevel exceeds a threshold value, or compare the counts of the selectenergy levels to the counts from corresponding select peak energy levelsof a reference spectrum. Each selected energy level is typicallyindicative of a particular element present in the piece of material. Insome known systems, the selected peaks are normalized, such that theresulting normalized peaks reflect the proportion of each element in thepiece of material. Typically, known methods require that the xrf of apiece of material is detected over a relatively long period of time suchas, for example, a second or more. Detecting over such a long periodensures that the selected peaks accurately reflect the proportion ofeach element.

[0135] The sorting algorithm described herein is a faster and moreflexible method of classifying a piece of material than those knownmethods described above. First, comparing the spectral pattern or imageof the detected xrf spectrum to the spectral pattern or image of storedreference spectra permits an accurate classification to be made evenwhen only a faint or weak image of the xrf spectrum of a piece ofmaterial is known (i.e. the detected spectral pattern takes the generalshape of the spectral pattern of a reference spectrum). Therefore,precise composition of a piece of material need not actually bedetermined (although it may be). Such a faint image results when arelatively limited number of x-rays or counts have been detected. Lesscounts result from shorter detection times. Thus, recognition of a faintimage permits a piece of material to be classified in shorter detectiontimes, substantially less than one second, possibly shorter than 10 ms.

[0136] Second, the sorting algorithm described herein permits a materialsorting system to have greater flexibility in sorting materials than doknown sorting algorithms allow. A user may select a random sample to useas a reference sample, establish the random sample as a referencespectra by detecting the xrf from the random sample for a relativelylong interval of time, for example 5 seconds, in order to eliminate anyrandom variations in the detected xrf, and store the xrf spectrumdetermined from the detected x-rays. The xrf spectrum of the randomsample can then serve as a reference spectra by which other pieces ofmaterial can be detected and compared against to determine whether thedetermined xrf spectra matches the reference spectra created from therandom sample. A user would not have to program the processing module toanalyze certain peak energy levels of the new reference xrf spectrum andfuture determined xrf spectra. In contrast, the sorting algorithm wouldcompare the spectral patterns without regard for peak energy levels.Known sorting methods require that sorting parameters be reconfigured toanalyze the peak energy levels of the reference xrf spectra anddetermined xrf spectra.

[0137]FIGS. 7A and 7B are each a diagram illustrating an illustrativeembodiment of using energy histograms to represent an x-ray fluorescencespectrum. Energy histogram 70 represents the comparison between the xrfspectral pattern of an unknown piece of material B08 and the xrfspectral pattern of chromeplate. Energy histogram 72 represents thecomparison between the xrf spectrum of B08 and the xrf spectrum of brass360. For illustrative purposes, the xrf spectral pattern of B08 isrepresented as a discrete energy counts, while the xrf spectral patternsof reference materials chromeplate and brass 360 are represented as acurve. For example, in energy histogram 70, 74 represents a discreteenergy count of B08.

[0138] The reference spectral curves 73 and 75 illustrate the fact thesespectral patterns were constructed from xrf collected over asignificantly longer collection interval than the detected pattern.Thus, the reference curves 73 and 75 are a more complete image of theirrespective xrf spectra than the faint image presented by the energycounts of B08.

[0139] The energy histograms 70 and 72 indicate that the unknownmaterial B08 is a piece of brass, the xrf of which was collected over arelatively brief interval of time such as, for example, 50 ms. Thereference materials chromeplate and brass 360, on the other hand, arecollected over a relatively long period of time, for example 5 seconds.As can be seen from the energy count histogram 72, from the energyhistogram itself and from the information panel 78, the brass reference,brass 360, is a very close match to the brass sample B08. The lowerright box of the information panel 78 indicates that the vector dotproduct produced from the comparison of these two spectral patterns is0.961. On the other hand, as shown by energy histogram 70, the chromeplate reference is not a very close match for the brass sample B08. Thisis indicated visually in the energy count histogram itself and also bythe vector dot product of 0.292 indicated in the lower right hand box ofthe information panel 76.

[0140] In FIGS. 7A and 7B, energy peaks of various elements present inthe materials are identified. For example, nickel (Ni) has an energypeak at 7.48 keV. As discussed above, known systems are typicallylimited to analyzing only the energy peaks, such as those shown in theenergy histograms of FIGS. 7A and 7B. These energy peaks are highlyindicative, however, of the composition of the reference material or thesample material. The partial dot product calculated between two energypeaks, comprising the multiplication of the normalized energy countsfrom each spectra at these energy peaks, has a greater impact on theoverall vector dot product than the partial dot products produced bymultiplying lower energy counts. Thus, the sorting algorithm describedherein, although considering a large range of energy levels, stillstatistically gives more weight to the peak energy levels characteristicof the elemental materials included in a material.

[0141] Returning to FIG. 4, the sorting application 35 accesses spectraldata from the spectrum acquisition module 33 and uses the data toexecute the sorting algorithm described above to determine which of theair jets 13-17 to activate in accordance with the classification of thepiece of material. The sorting application 35 may also store data in anon-volatile computer readable medium 41 such as, for example, adatabase. The database may be implemented with Microsoft Access, Cybase,Oracle, or other suitable commercial database systems. Such data mayinclude xrf spectra received from the spectrum acquisition module 33,sorting parameters, and the results of comparisons, e.g., dot products,between detected xrf spectra and reference xrf spectra. Once the data isstored in a database, such data may be analyzed using known databaseanalysis tools, such as a query language such as, for example, MicrosoftSQL.

[0142] The sorting application 35 also sends data to and receivescommands from a user interface 37 that may provide a visual display to asystem user on a video display device such as a monitor 43. The detailsof the graphical display produced by the user interface 37 is describedin more detail below in connection with FIG. 8.

[0143] In an illustrative embodiment, the sorting application 35executes at a real time rate, the functionality required by the sortingalgorithm executed by the sorting application 35 being separate from theuser interface 37. In an illustrative embodiment, the xrf processingmodule 9 runs an operating system on a computer such as, for example,WindowsNT®, a general-purpose operating system. Other known commercialoperating systems suitable to implement the sorting application 35 andthe user interface 37 may be used. In an illustrative embodiment, thedelays in timing uncertainties introduced by WindowsNT affect only theuser interface and not the sorting algorithm. In an illustrativeembodiment, all software system components are written for WindowsNT 4.0using Microsoft Visual C++ and Imagination Systems' HyperKernelreal-time extension. The Sommer application discloses source code thatmay be used to implement the sorting application 35.

[0144] In an illustrative embodiment, the sorting application 35executes on a real-time operating system.

[0145] In an alternative illustrative embodiment, the sortingapplication 35 is a real-time module that executes “underneath” theoperating system, and contains the entire sorting algorithm as well asany necessary sorting-hardware references. A real-time extension suchas, for example, the Imagination System's HyperKernel, of the Windows NToperating system may provide guaranteed real-tine control that isisolated from the non-deterministic delays introduced by ageneral-purpose task scheduler. HyperKernel library functions may beused for unrestricted access to an ejector air valve controller 42, andto registers of external hardware, such as a hardware illustrativeembodiment of the spectrum acquisition module 33.

[0146] The sorting algorithm described herein requires that spectra becaptured and processed at a precise rate with millisecond accuracy. Thespeed and precision of this execution are functions of the actual timefor executing the algorithm code, and the scheduling of the timed eventsin a multi-tasking environment. If the time required to execute thealgorithm were to exceed an inter sample period, then an auxiliaryembedded processor would be required. If a host computer has sufficientbandwidth to execute the algorithm within the required time, theoperating system must also ensure that the algorithm's tasks are notdelayed by tasks from other application or system service processes.

[0147] The second requirement is often the most difficult to satisfy.Although, contemporary PC hardware provides sufficient processing powerto execute all but the highest data-rate or most calculation-intensivealgorithms, general purpose multi-tasking operating systems, likeWindows NT, cannot guarantee real-time millisecond-precision service forthe algorithm's code. In an illustrative embodiment, a separate embeddedprocessor board is used to guarantee real-time execution of the sortingalgorithm, even when the host CPU may have adequate bandwidth. Inanother illustrative embodiment, a real-time extension to WindowsNT isimplemented to provide guaranteed time-slices to the sorting algorithm.The real-time extension allows the algorithm to be implemented as amulti-threaded application system with guaranteed sub-millisecondreal-time precision, so that the operating system (and its extension)scheduler satisfies the second requirement. The result is a xrfprocessing module 9 that can support the sorting algorithm without thecost of an additional embedded processor board.

[0148] The sorting algorithm executed by the sorting application 35requires that xrf be detected, the spectral pattern determined, and thepiece be of material be classified over short time intervals such as,for example, less than a second. The processing speed of most of today'scommercial PCs permits execution of the sorting algorithm in less than 1ms. Even a computer system implementing a 166 megahertz Pentiumprocessor can execute the sorting algorithm in less than 2 ms if run asa single non-interrupted thread of execution. The x-ray detector 27,however, requires 10 ms to 50 ms to acquire the spectrum, depending onthe intensity of the x-ray source 47, the respective distances betweenthe x-ray detector 27, the x-ray source 47, and the piece of material 25during detection, the composition of objects within the x-ray chamber,the conditioning of the x-ray detection and irradiation, the duration ofthe detection, and various parameters of the x-ray detector 27. Thus,the speed of the entire process is essentially limited by theacquisition time for the spectra.

[0149] The amount of xrf detected from a piece of material depends onthe detection time, which depends on the size of the piece of materialand the time the material spends in the detection area. Systems thatrely on the number of energy counts, as opposed to the proportionalrelationship between energy counts must know the size of the piece ofmaterial and the time spent under the x-ray detection device by thematerial. The high speed material sorting system and process describedherein may be used to sort materials of various sizes because thesorting algorithm depends on the proportions of the energy counts asopposed to the volume of the energy counts. Further, the sortingalgorithm can classify a piece of material from the recognition of afaint image of the spectral pattern of the piece.

[0150] Further, because x-rays are detected and an xrf spectrum isdetermined at a much faster rate, cumulatively, and because less x-raysare needed to classify a piece of material, pieces of materials as smallas {fraction (1/4)} inch may be classified at rates fast enough to makethe sorting and recycling of such pieces economically valuable. Size asused herein to describe the size of a piece of material means thelargest diameter of the piece of material in any dimension.

[0151] A problem with known material sorting systems, where pieces ofmaterials are conveyed along a conveyor belt, is that it is difficult todetect specific elements that fluoresce at low energy levels because thex-rays from these elements are so weak that the x-rays are absorbed byair before reaching a detector. For example, aluminum is difficult todetect because it fluoresces at energy levels below 2 kev, and thesex-rays are mostly absorbed by air before reaching an x-ray detector.Although the proceeding example uses aluminum for illustrative purposes,the example applies analogously to other elements that fluoresce at lowenergy levels. One solution is to put the x-ray detector closer to thepiece of material that includes the aluminum. However, when conveyingpieces of materials of variable size along a conveyor belt, the x-raydetector must be kept at a distance sufficient to accommodate thelargest possible size of a piece. Thus, small pieces may be further awayfrom the x-ray detector than larger ones.

[0152] In an illustrative embodiment of a high speed sorting ofmaterials, a piece of material comprising aluminum, or any element thatfluoresces at low energy levels, may be classified by recognizing thespectral pattern of the material as a whole. For example, aluminum maybe classified by the spectral pattern of its alloys by storing thespectral pattern of aluminum alloys as reference spectra, and mapping anair jet to each reference spectra. In an illustrative embodiment, if itis desired to sort all aluminum alloys into a common bin, multiple airjets may be mapped to a common sorting bin. The high speed materialsorting process as described herein may be executed, and pieces ofaluminum alloy may be recognized and sorted in accordance with thesorting algorithm.

[0153] In an illustrative embodiment of a high speed material sortingsystem, multiple sorting systems may be used in parallel, each sortingsystem optimized for a particular classifications of materials orparticular piece sizes. For example: a first system may sort pieces ofmaterial having a size from approximately {fraction (1/4)} inch toapproximately {fraction (5/8)} inch; a second system may sort pieceshaving a size from approximately {fraction (5/8)} inch to 4 inches; anda third system may sort pieces between 4 inches and 12 inches. Prior tosorting, a feedstock of materials could be pre-sorted into feedstocks,one for each size category. For each size-specific system, variousparameters could be optimized for the size of the materials it sorts.Parameters that may be adjusted include: the width and length of thebelt; the width and height of the chamber; the speed of the belt; thedistance between the x-ray source and the detection area, the distancebetween the x-ray detector and the detection area; the power of thex-ray source resulting in the intensity of the irradiated x-rays; theresolution of the determined spectra; the reference spectra; the numberof reference spectra; the threshold value for each spectra; the numberof sorting bins; the mapping of reference spectra to sorting bins, etc.

[0154] In an illustrative embodiment of a high speed materials sortingsystem, multiple x-ray detectors may be used. Such x-ray detectors maybe all be aimed at the same detection area, or may be aimed at differentdetection areas. The x-rays detected by the multiple detectors may allbe caused by a common x-ray source or multiple x-ray sources, where thex-ray detectors may be placed in series along the path of the conveyorbelt. Using multiple x-ray detectors allows for the gathering of morexrf to produce a more accurate spectral pattern of a piece of material,thus reducing the effects of random variations inherent with detectingx-rays.

[0155] In an illustrative embodiment of a high speed materials sortingsystem, materials may be sorted using a type of binary sort. Forexample, as opposed to the air jets 13-17 ejecting pieces of materialsinto sorting bins 18-22, the air jets can be used to eject the piece ofmaterials onto additional conveyor belts that lead to additionalsorting.

[0156]FIG. 9 is a block diagram illustrating an example illustrativeembodiment of a binary sort. In a first stage of the binary sort,materials may be sorted into metals 120 and non-metals 122 by a materialsorting system such as, for example, the high speed material sortingsystem 1 of FIG. 1. The system may eject metals onto a first belt forconveying metals into a material sorting system for sorting metals, andeject non-metals onto a second belt for conveying non-metals into amaterial sorting system for sorting non-metals. To implement this firstsort, the reference spectra of each sorting system and their respectivethreshold values may be selected such that the each sorting system isdesigned to differentiate between metals and non-metals. Selecting aproper threshold for a particular sort is described above with respectto the sorting algorithm.

[0157] In another stage of the binary sort, non-metals 122 may be sortedinto plastics 124 and ceramics 126, while metals 120 may be sorted intored metals 130 and other metals 128. The red metals 130 may then beseparated into copper 134 and brass 132. Each sort may be performedanalogously to the process described above with respect to the firststage of the binary sort.

[0158]FIG. 8 is a screen capture illustrating an illustrative embodimentof graphical display generated by a user interface 37. In anillustrative embodiment, the user interface 37 is a graphicalapplication written with standard Microsoft tools and libraries andexecutes strictly in NT user space. Other known commercial tools andlibraries may be used. The user interface functions for screenmanagement, keyboard or mouse input, and file I/O may be supported bythe standard WIN 32 libraries. This graphical application may runsimultaneously with other applications, and may be executed (andtask-swapped) by an NT task scheduler.

[0159] Although not shown in FIG. 4, an interface may be providedbetween the user interface 37 and the sorting application 35. Thisinterface passes commands between the user interface 37 and the sortingapplication 35, and the sorting algorithm results are passed back fordisplay by the user interface 37. A HyperKernel extension library maymanage a shared-memory region that is used to exchange data between theuser interface 37 (and user, or virtual memory space) and the real-timecode (in kernel, or physical memory space) of the sorting application35.

[0160] In this illustrative embodiment, the graphical display 80includes buttons at the top and left of the screen that are used forprogram control, setting parameters, and database management. Referencematerial button 94 allows a system user to set parameters for referencematerials. Data acquisition button 96 allows a user to set parametersfor data acquisition. The ejector control button 98 allows a user to setparameters for controlling ejection via the air jets. Results monitorbutton 100 allows a system user to set parameters for monitoring theresults of the sorting algorithm. Start button 102 permits a system userto start the sorting algorithm, while stop button 104 allows the systemuser to stop the sort algorithm. Check box 106 allows a user to enableor disable the ejectors. Configuration button 108 permits a system userto save the current configuration. Save dot product button 110 permits asystem user to save the results of a dot product between the xrfspectral pattern of a detected material and the xrf spectral pattern ofa reference material.

[0161] The histogram chart 82 displays a scrolling time histogram of dotproduct values taken with each reference spectra as a sample movesthrough the detection chamber 7. The numeric tables 86, 88, 90 on theright of the screen show dot product values and sorting thresholdsettings. The instant dot products table 90 shows the dot productsbetween a detected material and a reference material at a point in timeindicated by cursor 114, the cursor 114 being adjustable by a systemuser. The average dot product table 88 displays the average dot productacross the time interval displayed in the histogram chart 82. Thethreshold table 86 indicates the threshold value for the correspondingreference material of the reference material column 116.

[0162] The ejection destination chart 84 identifies the air jet/sortingbin corresponding to the classification of the piece of materialdetermined by the sorting algorithm. For example, in the histogram chart82, the dot products of the highest value at the instant indicated bythe cursor 114 is that of Cu 38 (copper), which, as indicated by theinstant dot product table, has a dot product of 0.903. In accordancewith this determination, the ejector designation chart shows that theCu/brass (copper/brass) ejector has been designated for the piece ofmaterial.

[0163] The high-speed metal sorting system and method disclosed hereinallows for hand shearing to be replaced by automated size reduction andsorting techniques such as shredding, grinding, crushing, airclassification, eddy-current separation, magnetic separation, andscreening. High-value metals, or other materials, can be liberated fromnon-metals or from lower value metals or materials to which they areadjoined. Once liberated and grouped by size, the particles may besingulated (particle by particle with spaces between particles) and fedonto conveyor belt 5.

[0164] The xrf processing module 9 may be implemented with a typicalcomputer system. The invention is not limited to any specific computerdescribed herein. Many other different machines may be used to implementthe xrf processing module 9. Such a suitable computer system includes aprocessing unit which performs a variety of functions and a mannerwell-known in the art in response to instructions provided from anapplication program. The processing unit functions according to aprogram known as the operating system, of which many types are known inthe art. The steps of an application program are typically provided inrandom access memory (RAM) in machine-readable form because programs aretypically stored on a non-volatile memory, such as a hard disk or floppydisk. After a user selects an application program, it is loaded from thehard disk to the RAM, and the processing unit proceeds through thesequence of instructions of the application program.

[0165] The computer system also includes a user input/output (I/O)interface. The user interface typically includes a display apparatus(not shown), such as a cathode-ray-tube (CRT) display in an input device(not shown), such as a keyboard or mouse. A variety of other known inputand output devices may be used, such as speech generation andrecognition units, audio output devices, etc.

[0166] The computer system also includes a video and audio data I/Osubsystem. Such a subsystem is well-known in the art and the presentinvention is not limited to the specific subsystem described herein. Theaudio portion of the subsystem includes an analog-to-digital (AID)converter (not shown), which receives analog audio information andconverts it to digital information. The digital information may becompressed using known compression systems, for storage on the hard diskto use at another time. A typical video portion of subsystem includes avideo image compressor/decompressor (not shown) of which many are knownin the art. Such compressor/decompressors convert analog videoinformation into compressed digital information. The compressed digitalinformation may be stored on hard disk for use at a later time.

[0167] One or more output devices may be connected to the computersystem implementing the xrf processing module. Example output devicesinclude a cathode ray tube (CRT) display, liquid crystal displays (LCD)and other video output devices, printers, communication devices such asa modem, storage devices such as disk or tape, and audio output. One ormore input devices may be connected to the computer system. Exampleinput devices include a keyboard, keypad, track ball, mouse, pen andtablet, communication device, and data input devices such as audio andvideo capture devices and sensors. The computer system is not limited tothe particular input or output devices used in combination with thecomputer system or to those described herein.

[0168] The xrf processing module 9 may be implemented on a generalpurpose computer system which is programmable using a computerprogramming language, such as “C++,” JAVA or other language, such as ascripting language or even assembly language. The computer system mayalso be specially programmed, special purpose hardware. In a generalpurpose computer system, the processor is typically a commerciallyavailable processor, such as the series x86 and Pentium processors,available from Intel, similar devices from AMD and Cyrix, the 680×0series microprocessors available from Motorola, and the PowerPCmicroprocessor from IBM. Many other processors are available. Such amicroprocessor executes a program called an operating system, of whichWindowsNT, Windows95 or 98, UNIX, Linux, DOS, VMS, MacOS and OS8 areexamples, which controls the execution of other computer programs andprovides scheduling, debugging, input/output control, accounting,compilation, storage assignment, data management and memory management,and communication control and related services. The processor andoperating system define a computer platform for which applicationprograms in high-level programming languages are written.

[0169] A memory system typically includes a computer readable andwriteable nonvolatile recording medium, of which a magnetic disk, aflash memory and tape are examples. The disk may be removable, forexample, a floppy disk or a read/write CD, or permanent, known as a harddrive. A disk has a number of tracks in which signals are stored,typically in binary form, i.e., a form interpreted as a sequence of oneand zeros. Such signals may define an application program to be executedby the microprocessor, or information stored on the disk to be processedby the application program. Typically, in operation, the processorcauses data to be read from the nonvolatile recording medium into anintegrated circuit memory element, which is typically a volatile, randomaccess memory such as a dynamic random access memory (DRAM) or staticmemory (SRAM). The integrated circuit memory element allows for fasteraccess to the information by the processor than does the disk. Theprocessor generally manipulates the data within the integrated circuitmemory and then copies the data to the disk after processing iscompleted. A variety of mechanisms are known for managing data movementbetween the disk and the integrated circuit memory element, and theinvention is not limited thereto. The invention is not limited to aparticular memory system.

[0170] Such a system may be implemented in software or hardware orfirmware, or a combination of the three. The various elements of thesystem, either individually or in combination may be implemented as acomputer program product tangibly embodied in a machine-readable storagedevice for execution by a computer processor. Various steps of theprocess may be performed by a computer processor executing a programtangibly embodied on a computer-readable medium to perform functions byoperating on input and generating output. Computer programming languagessuitable for implementing such a system include procedural programminglanguages, object-oriented programming languages, and combinations ofthe two.

[0171] The xrf processing module is not limited to a particular computerplatform, particular processor, or particular programming language.Additionally, the computer system may be a multi processor computersystem or may include multiple computers connected over a computernetwork. Steps 61-69 of FIG. 6 may be separate modules of a computerprogram, or may be separate computer programs. Such modules may beoperable on separate computers.

[0172] Having now described some illustrative embodiments, it should beapparent to those skilled in the art that the foregoing is merelyillustrative and not limiting, having been presented by way of exampleonly. Numerous modifications and other illustrative embodiments arewithin the scope of one of ordinary skill in the art and arecontemplated as falling within the scope of the invention. Inparticular, although many of the examples presented herein involvespecific combinations of method steps or apparatus elements, it shouldbe understood that those steps and those elements may be combined inother ways to accomplish the same objectives. Steps, elements andfeatures discussed only in connection with one embodiment are notintended to be excluded from a similar role in other embodiments.

1. A high-speed process for classifying a piece of material of unknowncomposition, the process comprising acts of: irradiating the piece withx-rays from an x-ray source, causing the piece to fluoresce x-rays;detecting the fluoresced x-rays with an x-ray detector; determining anx-ray fluorescence spectrum of the piece of material from the detectedfluoresced x-rays, wherein the detected x-ray fluorescence spectrum hasa spectral pattern; recognizing the spectral pattern of the determinedx-ray fluorescence spectrum; and classifying the piece based on therecognition of the spectral pattern, wherein the acts of detecting,determining, recognizing and classifying are cumulatively performed inless than one second.